1. Filed of the Invention
This invention relates to an exhaust gas treatment apparatus and particularly to an exhaust gas treatment apparatus for diffusion and deposition processes.
2. Description of the Prior Art
In semiconductor manufacturing process, a bare wafer has to go through hundreds of processes to be equipped with the desired function. The processes include microphotography, diffusion, deposition (particularly chemical vapor deposition, or CVD), etching and the like. These processes mostly require large amount of reaction gases, especially in the diffusion and deposition processes. While a small portion of the gases have reaction with the wafer, a great portion of the gases do not react with the wafer and become exhaust gases. The exhaust gases mainly include SiH4, SiH2Cl2, NF3, etc. They are highly toxic and should be properly treated to remove the toxicity to comply with industry standards before being discharged out.
In semiconductor industry nowadays, a commonly used treatment method for these toxic exhaust gases such as SiH4, SiH2Cl2, NF3 is to heat the exhaust gases to about 800.degree. C. and to mix with oxygen gas at high temperature to form powders of SiO2 compounds. The high temperature compounds then mix with cooling water to form vapor and waste water for discharging. An exhaust gas treatment apparatus usually has to be equipped with the function set forth above to handle the exhaust gases generated in the diffusion and deposition processes.
FIG. 1 illustrates a conventional exhaust gas treatment apparatus 10 which includes a main pipe 12, an U pipe 14 and a discharge pipe 16.
The main pipe 12 includes an inlet 121 at an upper end thereof, an outlet 122 at a lower end, a heater 123 surrounding the main pipe 12, a sprinkler 124 consisting of a plurality of nozzles and being located at a lower portion of the main pipe 12 in the center for providing cooling water required for exhaust gas treatment, and a scraper 125 which has a plurality of scraping knifes and being located at inside wall of the main pipe 12. The scraper 125 is driven by a transmission means 126 for removing lump type exhaust gas powder 20 adhering to the inside wall of the main pipe 12.
The U pipe 14 includes a pipe body 143, a first connector 141 located at one end of the pipe body 143 and connected with a bottom end of the main pipe 12, a second connector 142 located at another end of the pipe body 143, and a drain 144 located below the second connector 142.
The discharge pipe 16 has a bottom end connecting with the second connector 142, filters 161 located inside for filtering exhaust gases, and water nozzles 162 for spraying water to flush exhaust gas powder in the discharge pipe 16 to speed up exhaust gas treatment process.
Exhaust gases generated in the diffusion and deposition processes flow in the main pipe 12 through the inlet 121, and are heated by the heater 123 to form high temperature exhaust gas powders after having reacted with oxygen gas. The exhaust gas powder is then cooled by cooling water from the sprinkler 124 to form vapor and waste water which enter into the U pipe 14 through the outlet 122 and the first connector 141. Vapor continues to flow through the second connector 142 and is discharged out through the discharge pipe 16. Waste water is discharged out through the drain 144.
During exhaust gas treatment process, the inside wall of the main pipe 12 usually has exhausted gas powder deposited thereon which gradually forms lump type exhaust gas powder 20 sticking to the inside wall of the main pipe 12. This will reduce exhaust gas treatment efficiency. Therefore it needs to turn the scraper 125 to remove the lump type exhaust gas powder 20 from the inside wall of the main pipe 12 for maintaining the desired process. However the removed exhaust gas powder 20 tends to drop down in the U pipe 14 and clog the gas flow passage in the U pipe. It also impedes exhaust gas discharge operation. Hence how to improve exhaust gas treatment process is one of the ongoing R & D subjects in semiconductor industry.